Research On Flexible Manufacturing System Scheduling Problem Based On Petri Nets And Heuristic Search

Flexible manufacturing systems(FMSs)are a typical automated control system that can produce multiple types of products using shared resources such as robots,automated guided vehicles,and buffers,FMSs have many advantages,such as high efficiency,high quality,high flexibility,etc.With the advent of the Industrial 4.0 era,quickly responding to different production needs of users,and producing high-quality and personalized products in the shortest time becomes the most important core competitiveness of the factories in the future.As a result,there are a number of engineers and researchers working on scheduling flexible manufacturing system.Petri nets are a powerful modeling tool,they have both mathematical representation and graphical representation.Since Petri nets can effectively describe deadlock,concurrency,conflict,and so on in flexible manufacturing systems,they are a powerful tool for modeling and analyzing FMSs,and have been widely used in the scheduling problem of FMSs.This paper mainly studies the scheduling problem of FMSs based on Petri nets and heuristic search,The solution of this problem is given by the way of transition excitation sequences.The performance of the proposed solution is evaluated according to the makespan and the expanded markings of the corresponding transition sequences.The main research work is as follows:1.In order to find the optimal solution of the scheduling problem quickly and accurately,it is important to choose an efficient heuristic function.This paper introduces an improved heuristic function which is applicable to the system with alternative routing,and introduces a dynamic weighted scheduling algorithm.By using the heuristic function combined with the dynamic weighted scheduling algorithm,a scheduling scheme with less makespan and expanded markings can be obtained.2.According to the actual production environment and resource constraints of an FMS.We construct Petri net model of the system.Then,a scheduling strategy is obtained by using two different efficient heuristic functions and a dynamic weighted scheduling algorithm proposed in this thesis.Finally,experimented results are provided,the performance between the two heuristic functions to compare.3.According to the actual production requirements,some FMSs may have time constraint in special production environment(high temperature,high pressure,strong acid,strong alkali,etc.).In this case two scheduling algorithms under different time constraints are proposed.The proposed scheduling strategy can find a firing sequences such that all the time constraints are satisfied.Meanwhile,makespan and expanded markings are also considered to evaluate the performance of the proposed algorithms.